Automotive vehicles are commonly equipped with audio radios that receive and process signals relating to amplitude modulation/frequency modulation (AM/FM) antennas, satellite digital audio radio systems (SDARS) antennas, global positioning system (GPS) antennas, digital audio broadcast (DAB) antennas, dual-band personal communication systems digital/analog mobile phone service (PCS/AMPS) antennas, Remote Keyless Entry (RKE) antennas, Tire Pressure Monitoring System (TPM) antennas, and other wireless systems.
SDARS, for example, offer digital radio service covering a large geographic area, such as North America. Satellite-based digital audio radio services generally employ either geo-stationary orbit satellites or highly elliptical orbit satellites that receive uplinked programming, which, in turn, is rebroadcast directly to digital radios in vehicles on the ground that subscribe to the service. SDARS also use terrestrial repeater networks via ground-based towers using different modulation and transmission techniques in urban areas to supplement the availability of satellite broadcasting service by terrestrially broadcasting the same information. The reception of signals from ground-based broadcast stations is termed as terrestrial coverage. Hence, an SDARS antenna is required to have satellite and terrestrial coverage, and each vehicle subscribing to the digital service generally includes a digital radio having a receiver and one or more antennas for receiving the digital broadcast. The satellite and terrestrial coverage may be enabled via the implementation of a single antenna element, or alternatively, two antennas, each respectively receiving satellite and terrestrial-rebroadcast signals, which are typically referred to as a dual antenna element.
Besides SDARS, other vehicular communication systems may include one or more antennas to receive or transmit electromagnetic radiated signals, each having predetermined patterns and frequency characteristics. These predetermined characteristics are selected in view of various factors, including, for example, the ideal antenna radio frequency (RF) design, physical antenna structure limitations, and mobile environment conditions. Because these factors compete with each other, the resulting antenna design typically reflects a compromise as a result of the vehicular antenna system operating over several frequency bands (e.g., AM, FM, SDARS, GPS, DAB, PCS/AMPS, RKE, TPM, and the like) each having distinctive narrowband and broadband frequency characteristics and distinctive antenna pattern characteristics within each band. To accommodate these and other design considerations, a conventional vehicle antenna system can use several independent antenna systems while marginally satisfying basic design specifications.
A significant improvement in mobile antenna performance has been achieved by using an antenna that can alter its RF characteristics in response to changing electrical and other physical conditions. As seen in FIG. 1, one type of antenna system seen generally at 100 has been proposed to achieve this objective. The antenna system 100 is known as a self-structuring antenna (SSA) system. An example of a conventional SSA system is disclosed in U.S. Pat. No. 6,175,723 (“the '723 patent”), entitled “SELF-STRUCTURING ANTENNA SYSTEM WITH A SWITCHABLE ANTENNA ARRAY AND AN OPTIMIZING CONTROLLER,” issued on Jan. 16, 2001 to Rothwell III, and assigned to the Board of Trustees operating Michigan State University. The SSA system 100 disclosed in the '723 patent employs antenna elements that can be electrically connected to one another via a series of switches to adjust the RF characteristics of the SSA system as a function of the communication application or applications and the operating environment. A feedback signal provides an indication of antenna performance and is provided to a control system, such as a microcontroller or microcomputer, that selectively opens and closes the switches. The control system is programmed to selectively open and close the switches in such a way as to improve antenna optimization and performance.
Conventional SSA systems, such as the SSA system 100, may employ several switches in a multitude of possible configurations or states. For example, an SSA system that has 24 switches, each of which can be placed in an open state or a closed state, can assume any of 16,777,216 (224) configurations or states. Assuming that selecting a potential switch state, setting the selected switch state, and evaluating the performance of the SSA using the set switch state takes 1 ms, the total time to investigate all 16,777,216 configurations to select an optimal configuration is 50,331.6 seconds, or approximately 13.98 hours. During this time, the SSA system loses acceptable signal reception. Search time associated with selecting a switch configuration for a conventional SSA system may be reduced by incorporating a memory device with the conventional SSA structure. The memory device as discussed above is described in currently pending and related patent application Ser. No. 10/763,910 and invention record file number DP-309795 by the same inventor of the present invention. Essentially, the memory device evaluates a reduced number of the possible switch configurations for the SSA when a station, channel, or band is changed to reduce search times and provide improved SSA performance.
As seen in FIGS. 2A and 2B, known frequency-selective-surfaces (FSS), which are seen generally at 200a, 200b may include a plurality of dipole elements 201 (FIG. 2A) arranged in a generally vertical direction or a planar slot array 203 (FIG. 2B) in a conductive surface. When the dipole elements 201 are resonating, the array is completely reflective, and, when the slot elements 203 are resonating, the conductive surface is completely transparent As a result, the dipole array 201 acts as a spatial band-rejection filter and the planar slot array 203 acts as a spatial band-pass filter. Accordingly, when transmitting radiation is blocked, signals relating to a certain polarization, such as vertical, horizontal, LHCP, right-hand-circular polarization (RHCP), or the like, are reflected, transmitted, or absorbed by the FSS.
Although adequate for most applications, conventional FSS, such as those seen in FIGS. 2A and 2B, are designed to provide a surface with fixed characteristics designed to meet a well-defined application. For example, as stated above, when a vehicular antenna systems includes AM, FM, SDARS, GPS, DAB, PCS/AMPS, RKE, TPM, and other frequency bands received by an SSA or non-SSA systems, the FSS is designed to only reflect, transmit, or absorb a signal at one specific frequency or polarization. Therefore, in one example, when a system operates an SDARS application receiving both LHCP celestial-transmitted signals and vertically-polarized terrestrial-retransmitted signals, conventional FSS would have a fixed surface electromagnetic characteristic for the LHCP or vertically-polarized signal (i.e. energy)—not both polarizations, nor at different frequency bands when a channel or station is changed, nor for changing environmental conditions, such as, for example, the pitch of a vehicle on a hill that effects the elevation angle of the antenna(s), or the location of a vehicle in a lossy location such that trees or tall buildings obstructs the line of sight of the received signal(s).
Accordingly, it is therefore desirable to provide an improved FSS that dynamically changes its surface characteristics for a plurality of frequency bands, polarizations, and changing environmental conditions.